I. Field of the Invention
The present invention relates generally to valve cooling means and, more particularly, to an air cooled exhaust valve for an internal combustion engine or the like.
II. Description of the Prior Art
Valves, of the type utilized in the intake and exhaust passageways for internal combustion engines typically comprise an elongated stem having an enlarged valve head formed at one end of the stem. The stem is slidably mounted via a valve guide in an engine head while the enlarged valve head cooperates with a valve seat also secured to the engine head. The valve seat, which is annular in shape, is open at one axial end to a cylinder in the engine and to the exhaust manifold passage at its other axial end. Axial displacement of the valve stem moves the valve head away from and against the valve seat to respectively permit and block fluid communication through the exhaust passageway.
As is commonly known in the art, the valve head and lower portion of the valve stem, i.e., the portion of the valve stem extending into the exhaust or intake passageway, are subjected to high temperatures from the engine exhaust gases and this is particularly true for the exhaust valve. These high temperatures require these valves to be constructed of expensive, high quality steel in order to prevent thermal warpage of the valve. However, even when using high quality steel for the construction of the valve, the previously-known valves have been known to warp and even break in operation when subjected to particularly high temperatures.
There have been several previously-known fluid cooled exhaust valves for internal combustion engines but, for a number of reasons, these previously-known fluid cooled valves have not enjoyed widespread acceptance. For example, one such valve is disclosed in U.S. Pat. No. 1,731,222 to T. S. Blair in which pressurized air is emitted through a plurality of circumferentially spaced ports formed in and around the valve seat. This previously-known valve construction is disadvantageous, however, in that the valve seat is large and cumbersome and requires expensive casting and machining. Moreover, the Blair air cooled valve operatively cools the valve only when the valve is open.